This invention relates to idler pulleys used in combination with rubber belting. In particular the idler pulley is used in a positive drive system with a belt having internal driving lugs disposed on the inner surface of the belt. The pulley is particularly directed for use in a working environment where substantial amounts of debris, dirt and other fouling material is present and tends to accumulate on the working parts of the power transmission system. In particular agricultural harvesting equipment, conveyor belts and snowmobile tracks are applications where such conditions may prevail.
Where power transmission belts having internal driving lugs are employed there is typically a driving sprocket which transmits power to the belt. This invention relates to applications where the other support for the belt is an idler pulley as distinguished from a drive sprocket or pulley. The idler pulley must function to (1) guide the belt in its proper tracking orientation, (2) prevent the belt from slipping off of the driven idler, (3) support the belt such that the tensile bearing member in the belt is maintained in a flat plane to assure maximum load carrying capability of the belt. One known idler for a positive drive, lugged belt utilizes a groove positioned between two supporting sidewalls. The driving lugs of the belt are contained within the confines of the groove to maintain the proper tracking of the belt. The problem which is indemnic with these centrally grooved idler pulleys is that debris, snow, mud accumulates in the groove and may eventually build up to an extent that the belt is forced out of the groove and the power transmission ceases. Even if only a slight amount of debris accumulates in the groove, the belt will be supported only at the top of the tooth which is only a fraction of the transverse width of the belt. When only the edges the belt are supported, the tensile bearing member in the belt will be forced out of its planar configuration and into a troughed configuration where the outermost cords of the tensile member will be bearing virtually the whole load on the belt. The operating load will prematurely cause failure of the tensile bearing cords and substantially shorten the service life of the belt. One solution to this problem is to incorporate into the idler apparatus a scraper assembly which clears the groove of debris by positioning the scraper in close tolerance to the bottom of the groove and scraping the debris out as the idler rotates. The problems associated with this solution are that the scraper assembly must be in close proximity to the rotating idler and slight impacts may bind the scraper against the rotating idler thus causing excessive wear and power loss. Of course, if the binding is severe enough, either excessive heat buildup will cause fatigue and eventual failure of the idler or the whole idler will be frozen to a stop.
Another known idler is simply a disc which contacts the bottom of the belt carcass between adjacent longitudinal rows of drive lugs. This configuration causes the belt to sag at the edges due to the lack of support under those edges. This arching of the belt throws all the tensile stress on the centermost tensile members thus reducing the load carrying capacity and service life of the belt.
The idler pulley of this invention overcomes the functional disadvantages of conventionally known idlers by providing an idler configuration that positively supports the tensile member of the belt over a broader width. An object of the invention is to provide an idler which supports the drive lugs of the belt as well as one which frictionally engages and supports the portion of the belt between the drive lug rows. An advantage of the idler pulley is that the wider belt having multiple rows of driving lugs may be maintained in a flat plane to assure maximum power transfer by the belt. The idler of this invention is self-cleaning which prevents accumulation of debris and prevents the belt from being forced off of the idler of the desired track. Additional objects and advantages of the invention will be apparent to those skilled in the art.